As the first of the twin towers fell, NYPD officer Ada Resnick was enveloped in the massive cloud of debris that shrouded Lower Manhattan, the suffocating mix searing her eyes and lungs.

She thought she might die but emerged alive and spent a long day guiding survivors of the Sept. 11 terrorist attacks toward safety.

“I think we left for a couple of hours to just take a break and then pretty much for the next eight weeks or so we were working 12-hour days,” she said.

Thirteen years later, like many of the rescue and recovery workers who searched for bodies and cleared debris, she has lingering medical problems. She developed asthma and gastro-esophageal reflux disease, which is mild compared to the illnesses others have gotten, she said. But she is still worried about the future.

More than 2,300 New York City firefighters and other rescue workers have been diagnosed with cancers linked to the attacks and thousands have respiratory disease, diabetes, post-traumatic stress disorder and other ailments, according to the World Trade Center Health Program.

Now researchers at Mount Sinai Hospital are investigating two other possible killers-in-waiting: heart and kidney disease.

Resnick, who lives in Manhattan, is taking part in the two-year study, which began enrolling participants last month and for which the Icahn School of Medicine at Mount Sinai has received $1.1 million from the World Trade Center Health Program.

Doctors know that air pollution increases the risk of heart attacks, and those who rushed to the World Trade Center were caught in a toxic mix of jet fuel, asbestos, silica, cement dust, glass fibers and heavy metals. They already have higher rates of lung disease and gastrointestinal problems.

“Those people on 9/11 who were really in the cloud and who had high exposure for months afterward basically got this huge dose of air pollution at once,” said the study’s director, Dr. Mary Ann McLaughlin.

A preliminary study shows that those most exposed have higher levels of a protein in their urine, a condition called microalbuminuria that has been linked to a risk of heart disease, McLaughlin said.

“If you have that signal of leaking protein into the urine, then it can lead to really significant kidney disease,” she said. “No one so far has had the money to be able to really look at kidney disease even though I’m getting emails all the time now from people who have been diagnosed with bad kidney disease after 9/11 and the question is, ’Is this a link or is it just random?’”

McLaughlin just completed testing a group of mostly first responders, a relatively homogeneous group who are exposed to similar risks and have similar lifestyles. Five hundred and fifty of them are being asked to participate in the study so the researchers can look for the protein in their urine, assess their kidneys’ function and search for heavy metals such as lead, mercury and cadmium, exposure to which can lead to kidney disease, she said.

Former Police Officer Ada Resnick stands with her arms crossed outside Stuyvesant High School in the days after the Sept. 11 attacks.

Dr. Michael Crane, medical director of the World Trade Center Health Program at the Clinical Center of Excellence at Mount Sinai, noted one difficulty facing researchers: heart and kidney disease are illnesses that become more typical among older people.

“So it’s a hard thing to pull all those strings out and untangle them and trace them back to World Trade (Center),” he said.

New York City’s Health Department says that symptoms of post-traumatic stress disorder appear to be the most common health effect of Sept. 11. Survivors exposed to World Trade Center-related dust are more likely to develop lung problems and gastroesophaegeal reflux symptoms and those had multiple injuries and PTSD had a threefold higher risk of heart disease.

Three early cancer studies suggests that long-term monitoring of cancer occurrence is needed, according to the health department.

Resnick, 50, retired from the NYPD in 2006 and now works as an officer manager. On the day of the attack and immediately afterward, she did not fear for her health, but thought only about the job she had to do, she said. She wore a painter’s mask for a few hours, and remembers colleagues wondering what was in the air they were breathing, but she was mostly concerned about her eyes. She had had laser eye surgery two weeks earlier and was using eye drops.

She and her husband, who was also a police officer, worry that one or the other of them will get seriously ill, but the risks aside, she would do it all over again, she said.